A recent Washington Post poll -- conducted in the days before the latest episode, but after the Quran-burning incident and after American soldiers were caught urinating on the bodies of dead Taliban fighters -- reported that support for the war in Afghanistan among Republicans had dropped to record-low levels: 47 percent. Overall, 60 percent of Americans called the war not worth fighting.

"We have to either make the decision to make a full commitment, which this president has not done, or we have to decide to get out, and probably get out sooner," said GOP presidential candidate Rick Santorum not long after the news of the massacre broke. His remarks, noted by the media as a sign of growing Republican disenchantment in the war, echoed earlier ones by fellow candidate Newt Gingrich, who said the war "may, frankly, not be doable."

But according to numbers compiled by Gary C. Jacobson, a political scientist at the University of California, San Diego, since almost precisely the moment that President Obama took office -- and thus inherited command of a long and costly war started seven years earlier by his Republican predecessor -- support for the Afghan war among Republicans has been in rapid decline, while support among Democrats has largely leveled off.

Before Obama was elected in November 2008, Jacobson said, support for the war in Afghanistan had dropped among Republicans to about 75 percent, a steady but gradual 20 point decline from its initial high seven years earlier. Over the following three and a half years, GOP support for the war dove another 25 points to about 50 percent -- about twice the rate of decline.

Among Democrats -- whose support for the war had plummeted from about 80 percent to about 40 percent by the time President George W. Bush left office -- war disapproval slowed significantly after Obama's inauguration. The rate of decline began to level off a couple years earlier, approximately the time Obama, a Democrat, began to describe Afghanistan as the "good war" during the campaign.

"You don't get the Republicans really falling out as long as Bush was in the White House," said Jacobson, who has previously published his findings in Presidential Studies Quarterly, but made updated data available to The Huffington Post. "But once he was out they don't have the commitment -- they were committed to the president more than the policy."

William Howell, a professor of American politics at the University of Chicago, says the Afghanistan data supports a theory he has advanced for year: that partisan positions drive perceptions of wars.

"There is this notion that is in my view really mistaken that somehow domestic politics disappear when it comes to waging wars abroad," said Howell, who is the author of a book on how partisan identity in Congress can limit effective checks on presidential war powers. "There is lots of evidence that suggests that Democrats and Republicans think about war very differently. What's really interesting about the Afghan data is that we see that even when we fix the war, you have them responding in very different ways."

Furthermore, Jacobson says it can be very difficult to correlate changes in public opinion about a war effort with specific events in the war itself.

But Jacobson says that his numbers show that Republicans tended to support the surge more than Democrats, and that the McChrystal event would have taken place too late to immediately impact these numbers.

Instead, he says, the steep drop in support likely correlates more closely to a steeper drop-off in Republican approval of Obama generally during that time, and particularly as his health care plan was enacted.